Radioactive Materials from Atmospheric Testing Persist in Upper Atmosphere (Stratosphere), According to Swiss Researchers

More plutonium and cesium remain in the stratosphere than in the troposphere (which sits directly above the earth), though the amount is still very miniscule, measured in microbecquerels (1 microbecquerel = 0.000001 becquerel).

First, from BBC News (1/7/2014; emphasis is mine):

Nuclear weapon test debris 'persists' in atmosphere
By Rebecca Morelle

Radioactive particles from nuclear tests that took place decades ago persist in the upper atmosphere, a study suggests.

Previously, scientists believed that nuclear debris found high above the Earth would now be negligible.

However this research shows that plutonium and caesium isotopes are still present at surprisingly high concentrations.

The work is published in the journal Nature Communications.

Lead author Dr Jose Corcho Alvarado, from the Institute of Radiation Physics at Lausanne University Hospital in Switzerland, said: "Most of the radioactive particles are removed in the first few years after the explosion, but a fraction remains in the stratosphere for a few decades or even hundreds or thousands of years."

However, he said the levels were not high enough to pose a risk to human health.

Radioactive hangover

At the height of the Cold War, when the nuclear arms race was in full swing, weapons were being developed and tested around the world.

But more than 50 years on, their radioactive legacy remains.

While nuclear explosions initially throw material up into the air, scientists had thought that the radioactive particles would remain for a limited time.

In the troposphere (the lower layer of the atmosphere that sits directly above the Earth), the isotopes are removed fairly quickly, as they are "washed out" by attaching to rain or snow or are drawn down by gravity.

However, in the stratosphere (the layer that sits from about 10-50km above the Earth), the Swiss team believes that some particles become trapped.

"The concentrations we measured were in the order of about 1,000 to 1,500 levels higher in the stratosphere than in the troposphere," said Dr Jose Corcho Alvarado.

While the tests were carried out over Switzerland, the team said they expected similar levels would be found at the same latitude elsewhere around the world.

The scientists also found that this material can be moved around in the atmosphere by natural events such as volcanic eruptions.

For example, in 2010 after Iceland's Eyjafjallajökull volcano erupted, plutonium levels in the lower atmosphere increased.

While scientists say the long-term effects are not clear, the lead author Dr Jose Corcho Alvarado said: "It is important to say that this is not dangerous for the population."

He added that the nuclear debris could be tracked to find out more about how particles in the atmosphere move around.

The paper at the Nature Communications (peer-reviewed) (emphasis is mine):

Anthropogenic radionuclides in atmospheric air over Switzerland during the last few decades

Abstract:
The atmospheric nuclear testing in the 1950s and early 1960s and the burn-up of the SNAP-9A satellite led to large injections of radionuclides into the stratosphere. It is generally accepted that current levels of plutonium and caesium radionuclides in the stratosphere are negligible. Here we show that those radionuclides are present in the stratosphere at higher levels than in the troposphere. The lower content in the troposphere reveals that dry and wet deposition efficiently removes radionuclides within a period of a few weeks to months. Since the stratosphere is thermally stratified and separated from the troposphere by the tropopause, radioactive aerosols remain longer. We estimate a mean residence time for plutonium and caesium radionuclides in the stratosphere of 2.5–5 years. Our results also reveal that strong volcanic eruptions like Eyjafjallajökull in 2010 have an important role in redistributing anthropogenic radionuclides from the stratosphere to the troposphere.

The diagrams presented in the paper showing the activity concentration of plutonium (239+240) and cesium (137) in the atmosphere. The unit is microbecquerel/cubic meter (μBq/m3):

Plutonium:

Cesium:

(H/T Enformable)

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Long Shadow of Chernobyl (3): Dried Mushrooms from Italy Still Found With 170 Bq/kg of Cesium-137

One of the scientific researchers that I follow who goes by the name of "Tomynyo" on Twitter has been measuring all sorts of things after the Fukushima nuclear accident - soil accumulated on top of his apartment complex in Yokohama City with high levels of radioactive cesium to bamboo shoots and mushrooms served in the kindergarten lunch.

His latest tweets is not about the domestic mushrooms but about mushrooms from Italy:

イタリア製のボルチーニ茸6検体を測定したところ全ての検体からセシウム137が検出されました。 最大は170.3±18.0Bq/kg、最低は31.6±6.2Bq/kgでした。スーパーの乾椎茸はほとんど九州産ですから、普通に買える乾椎茸より汚染されていると思います　(link)

We measured 6 samples of [dried] Italian porcini mushrooms, and all samples were found with cesium-137. Maximum was 170.3±18.0Bq/kg, and minimum was 31.6±6.2Bq/kg. Dried mushroom you buy at a supermarket are almost all grown in Kyushu, so we think these Italian mushrooms are more contaminated than the dried Japanese mushrooms you can buy at a supermarket.

ボルチーニは水戻しした場合セシウム濃度は1/4になるそうです。... 3.11以前からそれなりの汚染された食品食べていた可能性があることは認識すべきです。(link)

If porcini mushrooms get rehydrated, the density of radioactive cesium would be one-fourths, we are told. We should recognize that we may have been eating food with certain levels of contamination even before March 11, 2011.

Just like the wood pellets from trees in Shikoku, Japan tested by one of my Twitter followers, cesium-137 is most likely from the atmospheric testing and the Chernobyl accident.

I happened on this video, supposed to be the raw footage of Chernobyl soon after the accident. I got scared watching workers with scant protection dumping loads of what looks like concrete debris:

Other "Long Shadow of Chernobyl" posts:

Long Shadow of Chernobyl: 224 Bq/kg of Cesium-137 in the Ashes from Burning Wood Pellets Made from Trees in Shikoku

Long Shadow of Chernobyl (2): German and Belarusian Researchers Say 64% of 229 Belarusian Children with High-Risk Thyroid Cancer in Complete Remission, 30% in Near-Complete Remission

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